Although the following description concerns its application for forming in particular, plane fuselage bulkheads, the invention clearly can be used in any other field where it is necessary or desirable to use slightly lightened sandwich type structures having good mechanical resistance and acoustic properties.
It is known that turboprop aircraft can pose sound insulation problems in the internal cockpit, especially regarding noises and vibrations generated by engines, propellers, aerodynamic noises, etc . . . .
Up until now, the problem of sound insulation has not been satisfactorily resolved, especially regarding the passenger cabin relative to the cargo portion and the specific purpose of the invention is to provide a new type of panel suitable for making bulkheads for passenger cabins.
These bulkheads need to be structural elements, that is, able to bear loads or stresses. The loads or stresses of bulkheads may be extremely significant. In fact, they must contain the luggage in the load bay should the aircraft be forced to make a crash-landing, or resist any abrupt depressurization of the cabin or load bay.
In addition, these bulkheads on the load bay side need to be aesthetic, that is, be decorated so as to match the rest of the cabin.
Currently, there are no panels available satisfying the usual constraints as regards lightness and fire-resistance, but also the above-mentioned various requirements.
The structural panels intended to reduce the effects of a crash-landing do not have any noise-deadening properties.
Moreover, there are sandwich type panels formed of a honeycomb core flanked on one side with a perforated metallic sheet and on the other side with a non-perforated metallic sheet used for their sound-reduction properties, for example as coverings at certain locations of the pod of a turbo-propeller so as to absorb, at least partially, the sound energy of high speed gas flows.
However, these structures have been revealed to lack solidity when it is desired to use them in severe environments for attenuating noise and preserving structural integrity.
U.S. Pat. No. 3,166,149 concerns panels of the type mentioned above but more sophisticated as regards the nature of the composite perforation covering mounted on one of the faces of the honeycomb core. This covering is firstly made of a glass fibre lattice preimpregnated with polymerized resin to stiffen the lattice before being bonded to one of the faces of the honeycomb. A sheet made of a porous material is then bonded to the outer face of the lattice, said sheet being covered with a thin decorative perforated and possibly movable covering, said covering not directly concerned with stiffening the unit. If the panel of U.S. Pat. No. 3,166,149 is considered as being able to be used as bulkheads, its structural rigidity and resistance are nevertheless inadequate to resist significant forces, such as those occurring during a crash-landing.
In addition, the materials generally used to form the honeycomb core and the non-perforated covering, namely an aluminum strip and an aluminum sheet respectively, result in composite structures possessing excessive surface mass.